In many industrial processes it is necessary to dispense a liquid to a number of machines or other pieces of equipment with as few interruptions as possible and with no contamination or gas bubbles in the liquid when it reaches its destination. One such situation is a semiconductor wafer fabrication facility, where photoresist must be dispensed to spinning machines which deposit it on the wafers. Hospitals and laboratories are other facilities where a liquid dispensing system of this kind is needed.
Photoresist is available in bottles or in sealed pouches made of a flexible membrane. To dispense the photoresist from a bottle, an ordinary tube is inserted into the liquid, and it is pumped from the bottle to a number of spinning machines. Because contamination may collect near the bottom of the bottle, the end of the tube is normally maintained an inch or so from the bottom of the bottle to avoid contaminating the flow to the spinning machines. In reality, the bottles are frequently discarded with as much as one-third of their contents remaining. Thus, an appreciable amount of photoresist is wasted. Moreover, each time the bottles are changed the spinning machine must be shut down.
An alternative arrangement for dispensing photoresist uses a pouch made of a flexible membrane. The pouch is inverted, with its mouth facing downward, and its mouth is connected to tubing which leads to the spinning machine. As photoresist is pumped through the tubing the pouch collapses, thereby preventing the development of a vacuum in opposition to the pumping action. While this arrangement substantially eliminates the contamination problem, bubbles can still enter the liquid each time the pouch is changed. If this happens, the entire fluid line from the pouch to the spinning machine must be purged to remove the bubbles.
In a third system, a reservoir is connected to a vacuum pump and photoresist is drawn into the reservoir from two different sources. The photoresist collects in the bottom portion of the reservoir and from there is directed through a number of outlets and tubes to the spinning machines. Since the photoresist must fall some distance upon entering the reservoir, bubbles may form. When they do, a certain amount of photoresist must be drawn out through a bleed valve to remove the bubbles. Again, photoresist is wasted.